﻿// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System;
using System.Security.Cryptography;
using System.Text;

namespace Microsoft.AspNetCore.Razor.Language;

internal class StringSourceDocument : RazorSourceDocument
{
    private readonly string _content;
    private readonly RazorSourceLineCollection _lines;
    private byte[] _checksum;

    public StringSourceDocument(string content, Encoding encoding, RazorSourceDocumentProperties properties)
    {
        if (content == null)
        {
            throw new ArgumentNullException(nameof(content));
        }

        if (encoding == null)
        {
            throw new ArgumentNullException(nameof(encoding));
        }

        if (properties == null)
        {
            throw new ArgumentNullException(nameof(properties));
        }

        _content = content;
        Encoding = encoding;
        FilePath = properties.FilePath;
        RelativePath = properties.RelativePath;

        _lines = new DefaultRazorSourceLineCollection(this);
    }

    public override char this[int position] => _content[position];

    public override Encoding Encoding { get; }

    public override string FilePath { get; }

    public override int Length => _content.Length;

    public override RazorSourceLineCollection Lines => _lines;

    public override string RelativePath { get; }

    public override void CopyTo(int sourceIndex, char[] destination, int destinationIndex, int count)
    {
        if (destination == null)
        {
            throw new ArgumentNullException(nameof(destination));
        }

        if (sourceIndex < 0)
        {
            throw new ArgumentOutOfRangeException(nameof(sourceIndex));
        }

        if (destinationIndex < 0)
        {
            throw new ArgumentOutOfRangeException(nameof(destinationIndex));
        }

        if (count < 0 || count > Length - sourceIndex || count > destination.Length - destinationIndex)
        {
            throw new ArgumentOutOfRangeException(nameof(count));
        }

        if (count == 0)
        {
            return;
        }

        _content.CopyTo(sourceIndex, destination, destinationIndex, count);
    }

    public override byte[] GetChecksum()
    {
        if (_checksum == null)
        {
            var charBuffer = _content.ToCharArray();
            var encoder = Encoding.GetEncoder();
            var byteCount = encoder.GetByteCount(charBuffer, 0, charBuffer.Length, flush: true);
            var bytes = new byte[byteCount];
            encoder.GetBytes(charBuffer, 0, charBuffer.Length, bytes, 0, flush: true);

            using (var hashAlgorithm = SHA1.Create())
            {
                _checksum = hashAlgorithm.ComputeHash(bytes);
            }
        }

        var copiedChecksum = new byte[_checksum.Length];
        _checksum.CopyTo(copiedChecksum, 0);

        return copiedChecksum;
    }
}
